Learn the Basics of the Kotlin Language
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In software programming, variables hold data and have a type. In Kotlin, variables can be read-only or mutable. In this demo, you’ll see how to initialize and work with variables in Kotlin. Later in this video, you’ll learn about code comments too. Start a new Kotlin Playground session or choose your preferred Kotlin environment to get started.
Using Variables
A variable holds data and has a name. In Kotlin, this is how variables are declared:
var day = "Monday"
val week = 2
lateinit var day : String
fun main(args: Array<String>) {
day = "Monday"
}
Mutable and Read-only Variables
To update a variable, it needs to be mutable. The previous example is mutable since it’s a var. To update it, remove the keyword and assign a different value of the same type:
fun main(args: Array<String>) {
day = "Monday"
println(day)
day = "Tuesday"
println(day)
}
val day = "Monday"
val day = "Monday"
day = "Tuesday" // Error
Basic Data Types
Basic types in Kotlin include integers, floating-point numbers, booleans, characters and strings.
Int
Integers represent numbers in Kotlin between -2,147,483,648 (-2^31^) and 2,147,483,647 (-2^31^ - 1). Here’s an example of an integer data type:
val amount = 100
println(amount::class.java.simpleName)
Long
If a value exceeds the limit for an Integer, it becomes a Long. Longs are also numeric values but have a higher capacity than Ints. Here’s an example of a Long:
val amount = 100L
println(amount::class.java.simpleName)
Floating-point
Floating-point types are numbers with decimals or fractions. Single-precision or decimal numbers holding 32 bits of data, are assigned the Floattype when creating variables. To initialize a floating point number explicitly, append an f to the number:
val amount = 100f
println(amount::class.java.simpleName)
Double
For higher or double-precision numeric data, use the Double class type. Double stores 64 bits of numeric data. To initialize a Double, use precision or a decimal point.”
val amount = 100.0
println(amount::class.java.simpleName)
val amount = 12_000_000_000
println(amount)
Boolean
The Boolean data type can be only one of two types: true or false. This makes it suitable for representing data that can only be in two states.
In the next example, the isWeekday variable tells whether it’s a weekday or not whiles isHoliday tells whether it’s a holiday or not:
val isWeekday = true
val isHoliday = false
Character
Characters represent single-character symbols and numbers. They’re instantiated using single quotes ' and must contain one character or two if it’s a special character:
val grade = 'A'
val newLine = '\n'
print("Monday")
print(newLine)
print("Tuesday")
String
Strings represent text. Strings are a sequence of characters put together and are initialized with double quotes ". They may or may not contain any characters.
val message = "End of the program!\nSee you next week."
println(message)
val message = """
End of the program!
See you next week.
"""
println(message)
Comments
Comments are a way to leave notes in your code. Comments are not interpreted as part of the code and can be short or long. For short comments, write your notes after // followed by a space. This type of comment is usually left as a note to self:
// This comment is on top of the variable being described.
const val WEEKLY_INTEREST = 100 // This comment is beside the variable being described.
/** This is known
as a block comment. */
const val WEEKLY_INTEREST = 100
/** This comment is a longer comment giving further information about the variable. */
const val WEEKLY_INTEREST = 100
/**
* This comment is longer.
* It has more information.
*/
const val WEEKLY_INTEREST = 100
/*
This comment is longer.
It has more information.
This is a valid comment block, but cannot be used with automatic document creation tools.
*/
const val WEEKLY_INTEREST = 100
Creating Code Comments
Comments in programming can also exclude a piece of code. Comments aren’t interpreted by the compiler, so they won’t have any effect on the output of the program. Consider the following example:
// const val WEEKLY_INTEREST = 100 /* This code is said to be commented out.*/